Indentation creep behavior of a direct-filling silver alternative to amalgam

Amalgam creep has been identified as a key parameter associated with marginal breakdown and corrosion. The aim of this study was to evaluate the time-dependent deformation (creep) of a novel silver filling material as an alternative to amalgam. We made the silver specimens by pressing a precipitated powder at room temperature to a density that can be achieved in clinical hand consolidation. The surface of the silver was either polished or burnished. To examine local contact creep and the effect of surface finishing, we used an indentation creep method in which a Vickers indenter was loaded on the specimen surface at a load of 10 N with dwell times of 5 sec to 6x10(4) sec. We used a bonded-interface technique to examine subsurface creep mechanisms. The flexural strength (mean+/-SD; n = 10) was 86+/-20 MPa for amalgam, 180+/-21 MPa for polished silver, and 209+/-19 MPa for burnished silver-values which are significantly different from each other (family confidence coefficient = 0.95; Tukey's multiple-comparison test). Indentation creep manifested as hardness number decreasing with increased dwell time. With dwell time increasing from 5 sec to 6x10(4) sec, the hardness number of amalgam was reduced by approximately 80%; that of the polished silver and the burnished silver was reduced by only 40%. Subsurface creep in amalgam consisted of the shape change of the alloy particles from spherical to elongated shapes, and the separation of matrix grains from each other, possibly due to grain-boundary sliding. Creep of the polished silver occurred by densification reducing porosity and increasing hardness; that of the burnished silver occurred by the displacement of the burnished layer. These results suggest that, due to creep-induced subsurface work-hardening and densification, the consolidated silver exhibits a higher resistance to indentation creep than does amalgam. The hardness number of silver approaches that of amalgam after prolonged indentation loading.     

Dental care in autism

The syndrome of autism is not characterized by typical orofacial features. Regarding caries experience, no differences with the normal population are found. The dental health situation on the other hand, depends upon the care devoted to oral hygiene and when necessary, upon the auxiliary help of parents and educators. As far as dental care is concerned, the autistic patient is inherently unresponsive to demonstrations, resists eye-to-eye contact and will frequently resist any effort to establish personal contacts with the dental personnel. Patient management will therefore be qualitatively different from person to person and shall be based on a unique management of the behavioral characteristics. Where the classical 'tell, show, do"-method fails, the 'tell, show, FEEL, do"-method will lead to a successful approach.     

The future of dental amalgam: a review of the literature. Part 1: Dental amalgam structure and corrosion

This is the first article in a series of seven on the future of dental amalgam. Dental amalgam is still the most useful restorative material for posterior teeth and has been used successfully for over 100 years. The history of dental amalgam since its introduction in 1819 and the controversies about its use between 1834 and today are described. The composition of the various dental amalgams in clinical use today are then reported. It finally covers the corrosion of amalgams since this is the means by which metals, including mercury, can be released.     

Dental care of the polymedication patient

With increasing frequency, ambulatory patients maintained on multiple medications are seeking dental care. Because new medications are approved for use each year and new interactions and side effects are regularly exposed for existing medications, it is important to keep current in this area. With the availability of regularly updated computer programs to help analyze accurate patient medication lists, the treatment of the polymedication patient has become much easier. The close, careful attention to patient medications should help prevent medical problems as well as reveal much about the patient's ability to withstand dental procedures.     

Dental care for the handicapped: general problems

In contrast to an increased oral health level in the Western countries, this improvement is not the case in age matched handicapped. The dental mutilation is generally related to periodontal problems (plaque, gingivitis, periodontitis, calculus), dental caries, traumatic injuries and self-injuring behaviour. Via a questionnaire, data from 88 institutions in Flanders were obtained. It became clear that there is a striking lack of oral health care and follow-up within institutions. There is a strong need for mouth hygiene instructions programmes for educators, parents, as well as for dentists involved in the special care of these patients.     

Interfacial bond strengths of amalgam bonded to amalgam and resin composite bonded to amalgam

A preparative method for the preparation of large peptides is described. An advantageous theoretical weight of peptide/weight of starting resin ratio (tPw/Rw) of about 0.3 was successfully experimented. The esterification of the first amino acid was realized with a racemization of less than 1%. The study of the coupling conditions led to the use of a diluted acylating mixture that allowed a 56% consumption of the amino acid derivatives (percentage use of amino acids) introduced in the synthesis. The cost analysis of the synthesis showed that the recovery of the amino acid derivatives was not worthwhile.     

Dental screenings using telehealth technology: a pilot study

BACKGROUND: This pilot study compared data obtained using traditional methods of visual dental screenings in a school setting with data obtained using an intraoral camera and transmitted to a distant location via telehealth technology. METHODS: For the study, 137 schoolchildren were screened using traditional methods. Two months later, 32 children were randomly selected and rescreened in a single day using the intraoral camera and the telehealth system. The measurement indices used were deft/DMFT. RESULTS: A comparison revealed no significant difference in the data collected by the two screening methods. The percentage agreement between the methods ranged from 89% to 100%. CONCLUSION: In under-serviced or remote areas, the telehealth system may allow for accurate identification of oral conditions and act as a means of consultation at a distance between specialists, general dental practitioners, dental hygienists and individual patients.     

水氯法从银阳极泥中提金

介绍了水氯法从银阳极泥中提金的基本原理、技术条件、设备配置以及技经指标,重点分析了氯化提金过程中的影响因素。该方法不仅适用于从银阳极泥中提金,也适用于从其他含金物料中提金,产品为国标1~#黄金。     

水氯法从银阳极泥中提金

介绍了水氯法从银阳极泥中提金的基本原理、技术条件、设备配置以及技经指标，重点分析了氯化提金过程中的影响因素。该方法不仅适用于从银阳极泥中提金，也适用于从其他含金物料中提金，产品为国标1#黄金。     

Perforation repair comparing mineral trioxide aggregate and amalgam using an anaerobic bacterial leakage model

The purpose of this study was to evaluate the ability of mineral trioxide aggregate (MTA) and amalgam to seal furcal perforations in extracted human molars using an anaerobic bacterial leakage model. Furcal perforations were made in 39 maxillary and mandibular human molars with a high-speed bur. These were randomly divided into two experimental groups of 18, with the remaining three teeth used as positive controls. Experimental group 1 was repaired with MTA and group 2 with amalgam. Three additional teeth without perforations served as negative controls. A dual chamber anaerobic bacterial leakage model was assembled. Brain heart infusion broth with yeast extract, hemin, menadione, and the chromogenic indicator bromcresol purple was used as the culture broth for Fusobacterium nucleatum. Eight of 18 amalgam samples leaked, whereas none of the 18 MTA samples leaked. MTA was significantly better than amalgam in preventing leakage of F. nucleatum past furcal perforation repairs.